The present invention relates to a shadow mask type color cathode ray tube, and in particular to a color cathode ray tube of the type having its shadow mask supported at its corners.
As image or video display devices, shadow mask type color cathode ray tubes are widely used which employ a shadow mask which is formed with a large number of electron-transmissive apertures and serves as a color selection electrode.
A color cathode ray tube of this kind has an approximately rectangular panel portion having a spherical, flat or approximately flat outer surface and an inner surface which is convex toward the outer surface. Formed on the inner surface of the panel portion is a phosphor screen comprised of phosphor elements of a plurality of colors (usually three colors of red, green and blue) in the form of dots, continuous strips, or slots.
An electron gun for projecting a plurality (usually three) of electron beams onto the phosphor screen is housed within a neck portion integrally connected to the panel portion via a truncated-cone-shaped funnel portion so as to form a vacuum envelope.
Closely spaced from the phosphor screen on the inner surface of the panel portion is a shadow mask structure comprising a support frame (or a mask frame, or referred to merely as a frame) of a generally rectangular shape conforming to that of the panel portion, a generally rectangular shadow mask which is convex toward the phosphor screen and is attached to the support frame at its periphery, and suspension springs to be adapted to engage studs embedded in an inner sidewall of a skirt portion of the panel portion.
In this shadow mask structure, suspension springs (also called plate-like springs, or leaf springs) are attached to the support frame along the sides of the support frame at at least three points of the support frame as by welding. The free ends of the suspension springs are formed with engagement holes which are adapted to engage the studs embedded in the inner wall (the inner sidewall of the skirt portion) of the panel portion such that the shadow mask structure is supported and spaced by a specified distance from the phosphor screen.
Usually the suspension springs are disposed at the four sides of the generally rectangular support frame, or at three of the four sides, and necessarily studs are embedded at positions of the inner sidewall of the skirt portion of the panel portion corresponding to the engagement holes in the leaf springs.
However, as the size of the viewing screen of color cathode ray tubes has been increasing recently, the weight of the shadow mask structure, and in particular of the support frame has increased and it is difficult for the above-described plate-like suspension springs to support the shadow mask structure properly and compensate for its positional deviations (so-called doming or the like) caused by thermal expansion of the mask structure sufficiently.
As one of means for reducing the weight of the shadow mask structure, and in particular of its support frame, a method is known to be effective which reduces the thickness and the width of the support frame and attaches suspension springs at the corners of the support frame.
FIG. 7 is a schematic plan view of the shadow mask structure having the suspension springs attached at its corners, as viewed from the electron gun side of the color cathode ray tube. A phosphor screen 4 is formed on the inner surface of a panel portion 1. A shadow mask 6 of the shadow mask structure is disposed at a specified distance from the phosphor screen 4, and suspension springs 8 attached to the four corners of a support frame 7 engage studs 9 embedded in the inner wall of the skirt portion of the panel portion 1. Lines of action of the suspension springs 8 are arranged approximately in parallel with the tube axis as described subsequently.
It is an object of the present invention to provide a novel color cathode ray tube capable of compensating for a doming phenomenon occurring in a shadow mask properly and improving efficiency in the operation of removing and remounting the shadow mask structure.
The following describes a representative one of configurations of the present invention.
To accomplish the above objects of the present invention, in accordance with an embodiment of the present invention, there is provided a color cathode ray tube comprising: an evacuated envelope including a generally rectangular shallow dish-like panel portion having a peripheral skirt portion, a tubular neck portion, and a funnel portion for connecting said peripheral skirt portion of said panel portion and said neck portion; an electron gun housed within said neck portion; a phosphor screen formed on an inner surface of said panel portion; a shadow mask structure closely spaced from said phosphor screen within said panel portion, said shadow mask structure comprising a generally rectangular peripheral frame, a generally rectangular shadow mask attached to said peripheral frame and having an apertured portion formed with a multiplicity of electron-transmissive apertures, and suspension springs attached to corners of said peripheral frame corresponding to corners of said panel portion; and a plurality of studs embedded in an inner wall of said skirt portion at said corners of said panel portion for supporting said shadow mask structure, wherein each of said suspension springs comprises: a base member including an electron-gun-side end portion attached to said peripheral frame, a sloped portion extending from said electron-gun-side end portion toward said inner wall of said skirt portion of said panel portion, and a first joint portion extending in a direction of a longitudinal axis of said color cathode ray tube from said sloped portion; and a spring member including a second joint portion fixed to said first joint portion of said base member, a resilient sloped portion extending at a tilt angle xcex8 from said second joint portion of said spring member toward said inner wall of said skirt portion of said panel portion, and a stud-engaging portion extending from said resilient sloped portion, bent from a plane of said resilient sloped portion toward said peripheral frame, and formed with an engagement hole to be engaged with a corresponding one of said plurality of studs, and a length L of said resilient sloped portion satisfies the following inequality: 20 mmxe2x89xa6Lxe2x89xa6an axial length of said frame, and said tilt angle xcex8 satisfies the following inequality: 0xc2x0xe2x89xa6xcex8xe2x89xa610xc2x0, where said tilt angle xcex8 is an angle measured in a state where said engagement hole is engaged with said corresponding one of said plurality of studs.
The present invention is not limited to the above configurations, and various changes and modifications may be made without departing from the scope of the invention as defined in the appended claims.